The invention is in the field of electronic reproduction technology and is directed to a method and to an apparatus for pixel-by-pixel and line-by-line, opto-electronic scanning of masters chucked on a scanner drum. Such a drum scanner unit, referred to below as a drum scanner, can be designed for scanning black-and-white or chromatic originals in reflected light and/or transmitted light.
A drum scanner for scanning transparency masters is composed, for example, of a rotating, transparent scanner drum onto which a transparency master to be scanned is chucked, a light source for pixel-by-pixel illumination of the transparency master, and of a scanner element having a scanner objective, a scanner diaphragm and an opto-electronic transducer for converting the scan light allowed to pass by the transparency master into an image signal that represents the luminance values of the scanned pixels.
The light required for the pixel-by-pixel illumination of the transparency master, for example, is transported via a light conductor from a light source located outside the scanner drum into the hollow-cylindrical interior of the scanner drum and is imaged onto the transparency master thereat as an illumination spot with a matching objective and a deflection mirror. The scan light modulated with the image content of the transparency original proceeds through the scanner objective into the scanner element located outside the scanner drum and is converted therein into an image signal by opto-electronic conversion.
The scanner element on the one hand and the optical elements on the other hand are respectively secured to an arm of a feed support designed U-shaped, whereby the arm carrying the optical elements projects into the scanner drum at the end face. For planar scanning of the transparency master, the feed support moves in the axial direction of the rotating scanner drum.
In order to be able to scan masters having different formats, scanner drums having different diameters are usually included in the equipment delivered with a drum scanner, these being chucked into the drum scanner dependent on the format of the master to be scanned. In this case, sets of lenses must be manually replaced at the feed support for optimum setting of the size of the illumination spot on the transparency master in order to compensate the different radial spacings between the central arm of the feed support and the generated surface of the respective scanner drum. For optimum focusing of the luminance-modulated scan light onto the scanner diaphragm, the scanner element of a traditional drum scanner is equipped with interchangeable lenses that must be manually pivoted into the beam path dependent on the diameter of the scanner drum employed. The employment of such sets of lenses and interchangeable lenses is relatively complicated.
It is therefore an object of the invention to improve a method and an apparatus for pixel-by-pixel and line-by-line, opto-electronic scanning of masters chucked on a scanner drum such that optical adaptations given employment of scanner drums having different diameters can be implemented in a simple way and automatically to the farthest-reaching extent.
This object is achieved by a method for point-by-point and line-by-line, opto-electronic scanning of a master, wherein the master is chucked on a scanner drum. A light spot is generated for pixel-by-pixel illumination of the master and is imaged onto the master as an illumination spot. The scan light is modulated with a content of the master, the scan light is focused with a scanner objective, and is converted into an image signal in an opto-electronic scanner element. The illumination spot, the scanner objective, and the scanner element implement the feed motion in a direction of the rotational axis of the scanner drum for scanning of the master. By employing scanner drums having different diameters, a size of the illumination spot is corrected by modifying an imaging scale of the illumination spot. An apparatus is also provided according to the invention for performing the above method steps.